Analyses of the plastic deformation of coated conductors deconstructed from ultra-high field test coils

Abstract REBCO coated conductors are now being used for building very high-field magnets with large electromagnetic stresses, both expected ones due to transport current J ⃗ × B ⃗ stresses and additional stresses resulting from the large screening currents inherent in wide tapes. Post mortem analyses of several recent test coils operated above 40 T show that significant conductor plastic deformation occurs, even for JBR stresses well below the ∼1 GPa yield of the Hastelloy substrate of the conductor. To investigate these deformation mechanisms, conductors were unwound after coil test and carefully examined with respect to their length-wise I c which revealed many areas of local damage. Regions of interest were examined by metallographic cross-section, Hall microscopy, magneto-optic imaging and scanning electronic microscopy. Important damage frequently occurred to the outer edges of panc…